For a steam turbine rotor provided as a central device of thermal power generation, for example, operation reliability, in addition to high temperature resistance and high pressure resistance, is required for improving the efficiency of thermal power generation by using steam of higher temperature and higher pressure. For this reason, as a steam turbine rotor, an integrally forged rotor of a high temperature material, namely of a 12% Cr steel material having excellent high temperature creep characteristics (12% Cr steel rotor) is used.
However, the 12% Cr steel rotor is disadvantageous to a low Cr steel rotor in that a carbide compound of carbon in the lubricant oil of the journal part and Cr is generated, and the sliding characteristic is impaired. By overlay-welding low Cr steel of about 1% on the surface of the journal part of the turbine rotor (build-up welding with low alloy steel), not only the above disadvantage is eliminated, but also occurrence of damages due to seizure or galling is prevented.
Patent Document 1 (JP 55-16744 A) discloses a turbine rotor that is free from breakage of a journal part. This turbine rotor is produced by preheating a cut cylindrical surface of the turbine rotor to a temperature of 200 to 250° C., conducting multilayer build-up welding with a welding bar composed of C: 0.1 to 0.3%, Mn: 1.5 to 2.0%, Cr: 0.05 to 0.1%, Si: 0.3% or less, and 0.03% or less of P and S, and a remainder of Fe, heating to 200° C., retaining at 120° C. for 10 hours, heating the entirety to 680° C., and then cooling to 300° C. at a rate of 5° C. per hour.
Patent Document 2 (JP 57-137456 A) discloses a turbine rotor in which torsion stress occurring in a bearing part is suppressed, and the shank surface is strengthened. This turbine rotor is featured in that an alloy composed of C: 0.05 to 0.35%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.00%, Mo: 0.10 to 2.00%, Cr: 0.30 to 2.80%, V: 0.05 to 0.35%, Ni: 0.50 to 4.00%, and a remainder of iron is build-up welded on the bearing part.
Patent Document 3 (JP 4-81293 A) discloses a 12% Cr steel steam turbine rotor shaft having sufficient strength without defects such as cold crack, hot crack and blowhole. In this 12% Cr steel steam turbine rotor shaft, the journal part is build-up welding metal composed of C: 0.11 to 0.17%, Si: 0.2 to 0.6%, Mn: 1.0 to 2.5%, P: 0.03% or less, S: 0.015% or less, Cr: 1.1 to 1.6%, Mo: 0.1 to 1.6%, V: 0.04% or less, and a remainder of Fe. Patent Document 3 describes production by conducting a lower build-up welding with a combination of a welding wire of low Cr and low Mo steel and a sintered flux by a submerged arc welding method, and subsequently conducting an upper build-up welding by a similar method.
Patent Document 4 (JP 6-272503 A) discloses a 5 to 13% Cr turbine rotor wherein a journal part has sufficient strength and includes little weld residual stress. This 5 to 13% Cr turbine rotor is produced by subjecting the journal part of the turbine rotor to a lower build-up welding with a carbon steel welding material, followed by an upper build-up welding with a low alloy steel welding material containing small amounts of Cr, Ni and Mo.
Patent Document 5 (JP 9-76091 A) discloses a method for build-up welding of a bearing part of a 12% Cr steel turbine rotor having high levels of fatigue strength and seizure resistance, and preventing occurrence of a microscopic weld defect. In this build-up welding method, on the lower side of the contact face of the 12% Cr steel turbine rotor with the bearing, a lower build-up layer side is welded with a welding material containing C: 0.03 to 0.2%, Si: 0.2 to 2.0%, Mn: 0.5 to 3.0%, Ni: 3.0% or less, Cr: 1.0 to 4.0%, a total of 0.05 to 1.5% of at least one selected from Al, Ti and Zr, H: 3.0 ppm or less, at least one selected from Nb, V, W, Ti and Mo satisfying a certain relational expression, and a remainder of substantially Fe, and an upper build-up layer side is welded with a welding material containing C: 0.03 to 0.2%, Si: 0.2 to 2.0%, Mn: 0.5 to 3.0%, Ni: 3.0% or less, Cr: 1.0 to 2.5%, Mo: 0.1 to 1.5%, Nb: 0.05% or less, V: 0.1% or less, a total of 0.05 to 1.5% of at least one selected from Al, Ti and Zr, H: 3.0 ppm or less, and a remainder of substantially Fe.
Patent Document 6 (JP 2011-11240 A) discloses forming a bearing part of turbine rotor by using a material for build-up containing C: 0.03 to 0.2%, Si: 0.2 to 1.0%, Mn: 0.5 to 3.0%, Ni: 0.1 to 0.5%, Cr: 1.0 to 2.5%, Mo: 0.1 to 1.5%, Ti: 0.008 to 0.05%, and a remainder of Fe.